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European frog-bit

(Hydrocharis morsus-ranae)

Photo of European frog-bit
Photo credit: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

A free-floating annual aquatic herb in the frog’s bit family. It can dramatically affect native aquatic life and limit recreational activities.

Overview

Other names for this plant include:
  • Common names: common frogbit
Ecological threat:
  • It invades shallow, quiet or slow-moving water; edges of lakes, rivers and streams; swamps, marshes, and ditches.
  • Forms large colonies of dense, floating mats that can dramatically affect native aquatic life and limit recreational activities.
 Overview map of prohibited classification in WI
Prohibited (red) counties

Classification in Wisconsin: Prohibited

Species Assessment Groups (SAG) were assembled to recommend a legal classification for each species considered for NR 40. The recommendation for European frog-bit was based upon this literature review [PDF] developed by the department.

Identification

Leaves: Usually floating; resemble tiny water lilies; kidney-shaped with long stems; 0.5-2.25” in diameter; smooth; often dark purple beneath; lateral veins are arching and make a 75-90 degree angle with the midvein; tissue containing air pockets are located mostly along the midvein. Lower leaf surfaces are dark purple in color.

Flowers: White; cup-shaped; three petals with yellow dots at base; bloom mid-summer.

Fruits & seeds: Rarely produces seeds and instead relies on vegetative reproduction.

Roots: Long, cord-like stolons form large floating mats of connected plants. It also forms turions.

Similar species: Often confused with American frog-bit (Limnobium spongia), a species whose leaves have lateral veins that make a 30-80 degree angle with the midvein, and whose leaf tissue contains large air pockets throughout.

Distribution

Currently, there have been no reports of European frog-bit in Wisconsin. Have you seen it? Send us a report.

Control

Mechanical: Other than hand-pulling, there are no known control methods.

Photos

View European frog-bit pictures in our photo gallery!

Resources

Sources for content: Links for more information: